An evaluation of overhead laser scanning to estimate herbage removals in pasture quadrats

The goal of this study was to test the utility of terrestrial laser scanning (lidar) as a means to estimate the dry weight and spatial distributions of herbage removals from small pasture plots. High resolution measurements of sward surface heights (SSH) were generated from lidar data acquired at close range over alfalfa (Medicado sativa subsp. sativa L.) and tall fescue (Festuca arundinacea Schreb. or Lolium arundinaceum (Schreb.) S.J. Darbyshire) pasture quadrats, before and after the collection of hand-plucked samples designed to mimic grazing by livestock. Removed herbage dry weights ranged from 3 to 65 g for n = 32 samples collected on 1 m2 quadrats, half in each pasture type. Volume change was calculated based on differences in SSH before and after plucking. Strong relationships were observed between volume change and dry weights of removals for both species (alfalfa r2 = 0.970, tall fescue r2 = 0.957). Contour maps gave detailed information on SSH before and after plucking, and the spatial distributions of herbage removed from field plots. Subject to further testing, lidar-based estimates could prove both reliable and non-invasive to livestock in grazing or herbage studies.